DESCRIPTION (Investigator's Abstract): This proposal aims to delineate the molecular and cellular neurobiology of the human neurodegenerative disorder, Niemann-Pick disease type C (NPC). NPC and its animal model, the cholesterol storage disorder (csd) mouse have been mapped to the pericentomeric region of chromosome 18, although the defective gene has not yet been identified. Two additional neurological mouse mutants, the ataxic (ax) and twirler (tw) are closely linked to the csd locus. A salient feature of NPC and csd is the abnormal accumulation of lysosomal cholesterol and other lipids which is associated with an attenuation of the normal homeostatic responses elicited by mammalian cells with lipoprotein uptake (stimulation of cholesterol ester synthesis, suppression of de novo cholesterol synthesis and down-regulation of LDL receptor activity). The investigators have established that processing of the 30 kD cholesterol binding protein, apolipoprotein (apo) D is deficient in cultured csd astrocytes and there is intracellular retention of a novel 46 kD apo D-immunoreactive protein that serves as a biochemical marker of the mutant cells. The investigators propose to determine the identity and role of this novel 46 kD apo D-immunoreactive protein in csd. To further investigate the role of apo D as an intracellular cholesterol transport protein in neural and non-neural cells, the investigators will use state-of-the-art biophysical techniques to investigate apo D-ligand interactions in cell free systems and in single live cells. Since apo D is a member of the lipocalin family of small hydrophobic ligand carrier proteins (examples of which include retinal binding protein, beta-lactoglobulin and odorant binding protein), these studies will provide new information on the structure- function correlates of apo D binding to cholesterol and related ligands as well as provide new insights into the mechanisms of ligand transport by lipocalins in general. The major phenotypic features of NPC and csd mouse reflect neurodegeneration with hypomyelination and a selective loss of cerebellar Purkinje cells. The investigators have established that secretion of the potent mitogen and growth factor, basic fibroblast factor (bFGF) from cultured astrocytes is deficient. This deficiency is associated with a maturational defect of oligodendrocytes in csd brain. Furthermore, expression of protein kinase C (PKC) which has been shown to be crucial for the expression of myelin protein genes during oligodendrocyte development, is restricted in csd brain. The investigators will therefore investigate the role of growth factors especially bFGF, as well as apo D, in oligodendroglial maturation and of PKC in the hypomyelination of csd brain. Finally, upon identification of the human NPC gene, the investigators propose to clone the mouse homolog of human gene in order to establish its relationship to the human mutation and to determine whether tw and ax are caused by a similar genetic defect(s). These studies will provide new insights into the molecular defect of human NPC and its mouse model, csd, as well as lead to a better understanding of the mechanisms of neurodegeneration in these inherited disorders.